The present invention relates to a pattern formation method and a pattern formation material, and more particularly, it relates to a pattern formation method for forming a resist pattern, used for forming a semiconductor device or a semiconductor integrated circuit on a semiconductor substrate, by using exposing light of a wavelength shorter than a 180 nm band and a pattern formation material used in the pattern formation method.
Currently, in fabrication of a mass storage semiconductor integrated circuit, such as a 64 Mbit dynamic random access memory (DRAM) and a logic device or a system LSI with a 0.25 xcexcm through 0.15 xcexcm rule, a resist pattern is formed by using a chemically amplified resist material including a polyhydroxystyrene derivative and an acid generator as principal constituents with KrF excimer laser (of a wavelength of a 248 nm band) used as exposing light.
Moreover, for fabrication of a 256 Mbit DRAM, a 1 Gbit DRAM or a system LSI with a 0.15 xcexcm through 0.13 xcexcm rule, a pattern formation method using, as exposing light, ArF excimer laser lasing at a shorter wavelength (of a 193 nm band) than the KrF excimer laser is now under development.
The resist material including a polyhydroxystyrene derivative as a principal constituent has high absorbance against light of a wavelength of a 193 nm band because of an aromatic ring included therein. Therefore, exposing light of a wavelength of a 193 nm band cannot uniformly reach the bottom of a resist film, and hence, a pattern cannot be formed in a good shape. Accordingly, the resist material including a polyhydroxystyrene derivative as a principal constituent cannot be used when the ArF excimer laser is used as the exposing light.
Therefore, a chemically amplified resist material including, as a principal constituent, a polyacrylic acid derivative or a polycycloolefin derivative having no aromatic ring is used when the ArF excimer laser is used as the exposing light.
On the other hand, as exposing light for a pattern formation method capable of coping with high resolution, an electron beam (EB) and the like are being examined.
When the EB is used as the exposing light, however, the throughput is disadvantageously low, and hence, the EB is not suitable to mass production.
Accordingly, in order to form a resist pattern finer than 0.10 xcexcm, it is necessary to use exposing light of a wavelength shorter than that of the ArF excimer laser, such as Xe2 laser (of a wavelength of a 172 nm band), F2 laser (of a wavelength of a 157 nm band), Kr2 laser (of a wavelength of a 146 nm band), ArKr laser (of a wavelength of 134 nm band), Ar2 laser (of a wavelength of a 126 nm band), soft-X rays (of a wavelength of a 13, 11 or 5 nm band) and hard-X rays (of a wavelength shorter than a 1 nm band). In other words, a resist pattern is required to be formed by using exposing light of a wavelength shorter than a 180 nm band.
Therefore, the present inventors have formed resist patterns by conducting pattern exposure using F2 laser (of a wavelength of a 157 nm band) on resist films formed from conventionally known chemically amplified resist materials respectively including a polyhydroxystyrene derivative represented by Chemical Formula A, a polyacrylic acid derivative represented by Chemical Formula B and a polycycloolefin derivative represented by Chemical Formula C. 
Now, a method for forming a resist pattern by using any of the aforementioned conventional chemically amplified resist materials and problems arising in the conventional method will be described with reference to FIGS. 2A through 2D.
First, as shown in FIG. 2A, the chemically amplified resist material is applied on a semiconductor substrate 1 by spin coating and the resultant is heated, so as to form a resist film 2 with a thickness of 0.3 xcexcm. Thereafter, as shown in FIG. 2B, the resist film 2 is irradiated with a F2 laser beam 4 through a mask 3 for pattern exposure. Thus, an acid is generated from the acid generator in an exposed portion 2a of the resist film 2 while no acid is generated in an unexposed portion 2b of the resist film 2.
Next, as shown in FIG. 2C, the semiconductor substrate 1 is heated with a hot plate at, for example, 100xc2x0 C. for 60 seconds.
Then, the resist film 2 is developed with an alkaline developer, thereby forming a resist pattern 5.
However, as shown in FIG. 2D, the resist pattern 5 cannot be formed in a good pattern shape, and there remains much scum on the semiconductor substrate 1. Such problems occur not only in using the F2 laser beam as the exposing light but also in using any of the other light of a wavelength shorter than a 180 nm band.
Accordingly, a resist pattern cannot be practically formed by irradiating a resist film made from any of the aforementioned chemically amplified resist materials with light of a wavelength shorter than a 180 nm band.
In consideration of the aforementioned conventional problems, an object of the invention is forming a resist pattern in a good pattern shape by using exposing light of a wavelength shorter than a 180 nm band with minimally producing scum.
The present inventors have studied the causes of the conventional problems occurring in using the conventional chemically amplified resist materials and have found the following:
First, the chemically amplified resist materials have high absorbance against light of a wavelength shorter than a 180 nm band. For example, a resist film with a thickness of 100 nm made from the chemically amplified resist material including a polyhydroxystyrene derivative as a principal constituent has transmittance of 20% at most against a F2 laser beam (of a wavelength of a 157 nm band).
Therefore, various examination has been made on means for improving the transmittance of a chemically amplified resist material against light of a wavelength shorter than a 180 nm band. As a result, it has been found that the transmittance of a chemically amplified resist material against light of a wavelength shorter than a 180 nm band can be improved when a unit of a polyhydroxystyrene derivative having hexafluoroisopropyl alcohol ((CF3)2Cxe2x80x94OH) on its side chain is introduced into a base polymer.
Furthermore, when any of the aforementioned chemically amplified resist materials, particularly the resist material including a polyhydroxystyrene derivative, is irradiated with light of a wavelength shorter than a 180 nm band, a reaction is caused regardless of the function of an acid, so that a hydrogen atom bonded to carbon located at the xc3xa1-position of the principal chain of the polymer can be released and that polymer radicals from which the hydrogen atoms are released can bond to each other to be crosslinked. As a result, the solubility of an exposed portion of the resist film in a developer is degraded. Therefore, means for preventing the crosslinking reaction of the principal chains of the polymer of a chemically amplified resist material has been variously studied. As a result, it has been found that the crosslinking reaction of the principal chains can be avoided by substituting an alkyl group or a chlorine atom for a hydrogen atom located at the a-position of the principal chain of the polymer.
Moreover, since the polymer has an aromatic ring on a side chain thereof, the dry etching resistance and the heat resistance of the resist film can be improved.
In addition, when hexafluoroisopropanol is introduced into an aromatic ring of the polyhydroxystyrene derivative, the transmittance against light of a wavelength shorter than a 180 nm band can be improved, and the solubility in a developer of a hydroxyl group from which a protecting group has been released can be improved. As a result, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be improved.
The present invention was devised on the basis of the aforementioned findings, and specifically provides pattern formation materials and methods described below.
The first pattern formation material of this invention comprises a polymer including a first unit represented by Chemical Formula 1 and a second unit represented by Chemical Formula 2; and an acid generator: 
wherein R1 and R3 are the same or different and selected from the group consisting of an alkyl group, a chlorine atom and an alkyl group including a fluorine atom; R2 is a protecting group released by an acid; and m is an integer of 0 through 5.
In the first pattern formation material, since the first unit has a hexafluoroisopropyl group and the second unit has a cyano group, the transmittance against light of a wavelength shorter than a 180 nm band can be largely improved. Furthermore, since an alkyl group, a chlorine atom or an alkyl group including a fluorine atom is substituted for hydrogen atoms located at the a-positions of the principal chains of the first and second units, the crosslinking reaction of the principal chains can be prevented, resulting in improving the solubility of an exposed portion of a resist film in a developer. Moreover, since an alcohol portion of the first unit has a trifluoromethyl group, the solubility of a hydroxyl group in the developer can be improved, so as to improve the solubility of the exposed portion of the resist film in the developer. Accordingly, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved. In addition, since the first unit has a benzene ring, the dry etching resistance can be improved.
The second pattern formation material of this invention comprises a polymer including a first unit represented by Chemical Formula 3 and a second unit represented by Chemical Formula 4; and an acid generator: 
wherein R1 and R4 are the same or different and selected from the group consisting of an alkyl group, a chlorine atom and an alkyl group including a fluorine atom; R2 is a protecting group released by an acid; and m is an integer of 0 through 5.
In the second pattern formation material, since the first unit has a hexafluoroisopropyl group and the second unit has a cyano group, the transmittance against light of a wavelength shorter than a 180 nm band can be largely improved. Furthermore, since an alkyl group, a chlorine atom or an alkyl group including a fluorine atom is substituted for hydrogen atoms located at the a-positions of the principal chains of the first and second units, the crosslinking reaction of the principal chains can be prevented, resulting in improving the solubility of an exposed portion of a resist film in a developer. Moreover, since an alcohol portion of the first unit has a trifluoromethyl group, the solubility of a hydroxyl group in the developer can be improved, so as to improve the solubility of the exposed portion of the resist film in the developer. Accordingly, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved. In addition, since the first and second units have a benzene ring, the dry etching resistance can be improved.
The third pattern formation material of this invention comprises a polymer including a first unit represented by Chemical Formula 5, a second unit represented by Chemical Formula 6 and a third unit represented by Chemical Formula 7; and an acid generator: 
wherein R1, R3 and R5 are the same or different and selected from the group consisting of an alkyl group, a chlorine atom and an alkyl group including a fluorine atom; R2 is a protecting group released by an acid; and m is an integer of 0 through 5.
In the third pattern formation material, since the first unit has a hexafluoroisopropyl group, the transmittance against light of a wavelength shorter than a 180 nm band can be largely improved. Furthermore, since an alkyl group, a chlorine atom or an alkyl group including a fluorine atom is substituted for hydrogen atoms located at the a-positions of the principal chains of the first, second and third units, the crosslinking reaction of the principal chains can be prevented, resulting in improving the solubility of an exposed portion of a resist film in a developer. Moreover, since an alcohol portion of the first unit has a trifluoromethyl group, the solubility of a hydroxyl group in the developer can be improved, so as to improve the solubility of the exposed portion of the resist film in the developer. Accordingly, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved. In addition, since the first and third units have a benzene ring, the dry etching resistance can be largely improved. Moreover, since the third unit has a hydroxyl group, the wettability is improved so as to improve the adhesion to the substrate, and the dissolving rate in an alkaline developer can be controlled by adjusting the ratio of the third unit in the polymer.
The fourth pattern formation material of this invention comprises a polymer including a first unit represented by Chemical Formula 8, a second unit represented by Chemical Formula 9 and a third unit represented by Chemical Formula 10; and an acid generator: 
wherein R1, R4 and R5 are the same or different and selected from the group consisting of an alkyl group, a chlorine atom and an alkyl group including a fluorine atom; R2 is a protecting group released by an acid; and m is an integer of 0 through 5.
In the fourth pattern formation material, since the first unit has a hexafluoroisopropyl group, the transmittance against light of a wavelength shorter than a 180 nm band can be largely improved. Furthermore, since an alkyl group, a chlorine atom or an alkyl group including a fluorine atom is substituted for hydrogen atoms located at the a-positions of the principal chains of the first, second and third units, the crosslinking reaction of the principal chains can be prevented, resulting in improving the solubility of an exposed portion of a resist film in a developer. Moreover, since an alcohol portion of the first unit has a trifluoromethyl group, the solubility of a hydroxyl group in the developer can be improved, so as to improve the solubility of the exposed portion of the resist film in the developer. Accordingly, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved. In addition, since the first, second and third units have a benzene ring, the dry etching resistance can be largely improved. Furthermore, since the third unit has a hydroxyl group, the wettability is improved so as to improve the adhesion to the substrate, and the dissolving rate in an alkaline developer can be controlled by adjusting the ratio of the third unit in the polymer.
Specific examples of the protecting group released by an acid represented by R2 in the aforementioned general formulas are those represented by Chemical Formula 11: 
The first pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, the first pattern formation material; irradiating the resist film with exposing light of a wavelength shorter than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
In the first pattern formation method, since the first pattern formation material is used, the transmittance against light of a wavelength shorter than a 180 nm band can be largely improved, the solubility of an exposed portion of the resist film in a developer can be improved, the dry etching resistance can be improved, and the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved.
The second pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, the second pattern formation material; irradiating the resist film with exposing light of a wavelength shorter than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
In the second pattern formation method, since the second pattern formation material is used, the transmittance against light of a wavelength shorter than a 180 nm band can be largely improved, the solubility of an exposed portion of the resist film in a developer can be improved, the dry etching resistance can be improved, and the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved.
The third pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, the third pattern formation material; irradiating the resist film with exposing light of a wavelength shorter than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
In the third pattern formation method, since the third pattern formation material is used, the transmittance against light of a wavelength shorter than a 180 nm band can be largely improved, the solubility of an exposed portion of the resist film in a developer can be improved, the dry etching resistance can be improved, and the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved. Furthermore, the wettability of the pattern formation material can be improved so as to improve the adhesion to the substrate, and the dissolving rate in an alkaline developer can be controlled by adjusting the ratio of the third unit in the polymer.
The fourth pattern formation method of this invention comprises the steps of forming a resist film by applying, on a substrate, the fourth pattern formation material; irradiating the resist film with exposing light of a wavelength shorter than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure.
In the fourth pattern formation method, since the fourth pattern formation material is used, the transmittance against light of a wavelength shorter than a 180 nm band can be largely improved, the solubility of an exposed portion of the resist film in a developer can be improved, the dry etching resistance can be improved, and the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be largely improved. Furthermore, the wettability of the pattern formation material can be improved so as to improve the adhesion to the substrate, and the dissolving rate in an alkaline developer can be controlled by adjusting the ratio of the third unit in the polymer.
In any of the first through fourth pattern formation methods, the exposing light can be light of a wavelength of a 110 through 180 nm band such as a Xe2 laser beam, a F2 laser beam, a Kr2 laser beam, an ArKr laser beam or an Ar2 laser beam; soft-X rays of a wavelength of a 1 through 30 nm band; or hard-X rays of a wavelength shorter than a 1 nm band.